For example, in equipment that operates underwater, since it is difficult to use an internal combustion engine or to lay electric wires, electric power stored in a storage battery is often used as a power source. A wireless power supply system disclosed in Patent Document 1 has been proposed as a wireless power supply system for charging a storage battery underwater.
In such a wireless power supply system, when a distance between a power-receiving coil and a power-transmitting coil increases, power supply efficiency decreases (see Patent Document 2). Accordingly, in order to perform stable supply of power, it is preferable that the positional relationship between the power-receiving coil and the power-transmitting coil be fixed.